Dr. Phil Metzger Profile picture
Director, Center for Microgravity Research & Education @UCF. Previous: co-founder of NASA KSC Swamp Works. Space Mining. Space Settlement.
Tomáš Kafka Profile picture Ireneusz Kozłowski Profile picture R. Chitwood 🇺🇸🇺🇸🇺🇸 Profile picture RJ Profile picture @AlgoCompSynth@universeodon.com by znmeb Profile picture 15 subscribed
Mar 18 10 tweets 2 min read
I’m not so sure. The link to the prior estimate is a paper that measures the “blast zone”, which is the region around a lander where the reflectivity of the surface has changed. We have never known exactly what causes this change. Is it from gas blowing the dust texture flat? /1 2/ Or is it from blowing dust plowing across the surface? Or from engine shutoff when the last sputter of the engine cause a low velocity blanket of dust to fly out to a much smaller distance than normal? The problem has always been that this blast zone is *too small* to be…
Mar 17 12 tweets 3 min read
Lots of discussion today on space radiation including errors like this one. This has confused water with regolith. Using too thin a layer of *regolith* creates secondaries, increasing the dose. But using water, or PTFE (lots of hydrogen), even very thin, always reduces the dose/1 2/ The thing about using regolith for shielding is that you use it when you are on the surface of a planet, and there’s so much available and you do t carry it on a spaceship so you have no reason to use a thin amount. It entirely solves the problem!

And…
Feb 25 22 tweets 6 min read
I could write a 50 page paper answering this :)

A few points in outline form only:

1) The rocket exhaust is expanding into vacuum, so viscosity breaks down, so the gas does not obey the Navier-Stokes equation, which is the basis of CFD (computational fluid dynamics) models. /1 2/ When I was at NASA, one of the things I was doing was writing solicitations to industry to write physics-based code to do CFD without Navier-Stokes. There are many ways to treat the fundamental physics (the Boltzmann Transport Equation) and they all work for different…
Feb 24 17 tweets 4 min read
About how the lunar environment makes everything tippier…

1) I’m sure the CLPS contractors know this and designed for it. My point is that the Moon does this to your hardware, so when things go wrong (as they do) then tipping happens more often than on Earth. /1 2/

2) There are different ways you can tip. For static stability, gravity makes no difference. You fall when you are so tilted that the center of gravity (cg) is outside of your footpad. I don’t know where the Nova-C has its cg, but crudely it could handle ~54 degrees tilt. Image
Feb 3 35 tweets 12 min read
I finally submitted this paper to Icarus (planetary science journal). I split it into two papers: “Erosion rate of lunar soil under a landing rocket, part 1: identifying the rate-limiting physics” and “…part 2: benchmarking and predictions.” The breakthrough was in part 1.
1/N 2/ It took 8.5 months from the breakthrough while sitting at McDonalds until I got the paper done. 😭 I had to re-do it several times. 💀

I’m not keeping the info secret before publication, so I’ll go ahead and tell a little here.
Jan 27 19 tweets 7 min read
This is a fun and fascinating thread. I’ll add one thought. Latif says that some objects are dynamical and move about but the “regular” planets & moons aren’t that way, but really it’s just a matter of timescales. Everything changes orbits. 1st read Latif’s thread then mine…🙂/1 2/ An example of a moon that changed orbits: Triton. It is currently a moon of Neptune but previously it was a primary planet orbiting the Sun directly (albeit a small planet…a dwarf planet like Pluto). Neptune captured it! Image
Jan 23 31 tweets 7 min read
This was a fun read but I have this response. The piece says that Turner’s Frontier Thesis is a strong motive of people who want to move civilization beyond Earth. But that’s not true. It is merely *adjacent* to the actual strong motives. Discarding it makes no difference. /1 2/ As the article explains. Turner’s thesis is that the US Western frontier created an open democratic society of self-reliant individuals with strong moral fiber. It says the western frontier values diffused back east to keep the rest of the US from falling into degeneracy, too.
Dec 31, 2023 9 tweets 2 min read
Here’s the problem with trying to respond to Dr. Kirkpatrick’s request. Many technologists (myself included) believe we have reached the point where technology is changing so fast we cannot even guess what it will look like beyond a few decades. Any alien civilization that…/1 2/ …is so far ahead of us that they could travel between stars is way, way beyond the point that it becomes completely unpredictable. Therefore, any models we might create for what the tech could look like (how they might get here, how they might refuel…) are unconstrained.
Nov 22, 2023 9 tweets 3 min read
Apologies for the crude markup (did this on my phone). Your eye can pick out these features better in the video than in a single snapshot, so watch the video and look for these annotated features (short thread). 1/N
Image 2/ Each nozzle has a plume (a jet) that is slightly mismatched relative to surrounding air pressure, so they oscillate in diameter, widening and narrowing to try to match pressure, but overshooting each time so they oscillate. These are the Mach diamonds.
Nov 3, 2023 4 tweets 1 min read
Just today I was advising a PhD student and told him something very similar. We were discussing experimental results that seem irrational, contrary to theory, and showing no pattern at all. Over the course of my career I’ve learned that whenever you’re in this situation… /1 2/…you have to tell yourself that nature is not irrational; there is always an explanation, and it can always be found. Someone will find it, and that person can be me.

If you don’t believe that, you won’t persevere and you won’t find the answer. But in my experience,…
Oct 6, 2023 9 tweets 3 min read
I got word today that our research into the Starship launch pad anomaly is being forwarded uphill to NASA HQ. They are focusing on what we learned about launch/landing pad failure modes and how we can make lunar landings safer. /1 2/ What we found is that the pressure that built up beneath the launch pad was comparable to a volcanic eruption when the buildup of hot gas that evolves from the magma busts apart the caprock and expels it. (Pic: Fagents & Wilson, Geophys J Int 113(2): 359.) Image
Aug 23, 2023 11 tweets 3 min read
Thanks to all who sent info on the Starship launch wind conditions. I haven’t responded to all the replies individually yet to express thanks since I was swamped with three proposals last week and now I’m on travel. HOWEVER,… 1/2 2/ …I have a new request for help.

Does anybody remember seeing the brown dust cloud that drifted north toward Port Isabel from the launch site? We need to estimate it’s altitude. Cloud height is hard to judge, but…
Aug 16, 2023 18 tweets 7 min read
#WeirdWednesday thoughts. Can civilization be studied like it is a **material** that forms naturally in the cosmos? What are the material properties of this bizarre material?

I'm wondering because papers that try to answer the Great Silence (or Fermi Paradox) treat it this way, and it is very helpful. 🧵 /1 2/ We can consider civilization to be a phase change of matter. Phase changes include melting, freezing, vaporization, and condensation. Matter is in one state, then something happens and it goes to another state.
Aug 8, 2023 26 tweets 8 min read
The UAP debates reminded me of a personal story about handling evidence and judging likelihood. I think this is interesting & amusing.

🧵:

On Shuttle mission STS-128 the rocket exhaust blew out 3,500 tiles from the side of the flame trench. /1 Image 2/ The bricks were smashing into each other as they blew, fragmenting into millions of pieces of all sizes. The results were devastating to the perimeter of the pad. This is what the security fence looked like about a kilometer away. See the brick fragments? 🤯 Image
Aug 1, 2023 41 tweets 8 min read
Lots of people are telling me that the radar observations make the aviator TicTac observations more likely an advanced vehicle, but tbh the radar observations are my biggest cause for doubt. (I used to be a radar/avionics engineer for NASA for many years chasing such anomalies.) 2/ Here are a few of the many weird things we saw on radars/avionics at NASA.

(1) for a while, we started getting weird signals on the Space Shuttle TACAN systems and we were in a NOGO for launch because of it. We went into emergency mode trying to figure out their source...
Jul 17, 2023 19 tweets 7 min read
Some clarification about the possible interstellar material from the ocean bottom — why scientists care.

Also, did you know that not just the elements of our world are stardust (interstellar), but even an important class of *molecules* here may be interstellar? /1 2/ The elements heavier than helium were made in the fusion and/or supernova of stars. It was swept into the disk that formed our Sun and planets. So people are pointing out that we already have interstellar material here. That’s true, but there is something else more interesting
Jun 12, 2023 23 tweets 8 min read
This is a well written piece by @SineadOS1 criticizing the hype that Starship radically lowering launch prices will send the space sector into hyper-growth. Mandatory reading to be informed, IMO, but I want to give a nuanced response… 1/n

ft.com/content/8c04df… 2/ Many of us space technologists have argued for years, long before Starship was even imagined, that space will grow to much more than the trillion dollar industry Sinead discusses. But we have argued this growth will not be overnight. It will take decades. /… Image
Jun 5, 2023 16 tweets 6 min read
Also in the arXiv now: our 2010 conference paper “Rocket Cratering in Simulated Lunar and Martian Environments.”

arxiv.org/pdf/2306.01078…

It reports 3 experiment campaigns: (1) reduced gravity soil erosion; (2) reduced gravity angle of repose; (3) rockets firing in deep soil. Image 2/ In the soil erosion tests we got a super clean result: in non-cohesive materials, erosion rate scales inversely to gravity. (That’s me on the aircraft floor doing the test. I hope you like our McGyver flashlights we duct-taped onto the box during the test, lol.) ImageImage
Jun 5, 2023 12 tweets 5 min read
Our 2010 paper is now in the arXiv:

“Soil Test Apparatus for Lunar Surfaces.”

We experimented with several hand-held soil testing tools and 4 different lunar soil simulants. An interesting discovery: one simulant did not behave like the others.

arxiv.org/pdf/2306.01080… Image 2/ This surprised us because the main factor in how a granular material behaves is it’s particle size distribution (PSD). All 4 lunar simulants had very similar PSDs matching real lunar soil, and yet one of them behaved completely unlike the others. Image
May 16, 2023 4 tweets 2 min read
Well today was a good day. After 25 years researching how rocket exhaust lifts soil, I think I finally got the main story put together. I will submit this to one of the prestige journals, I guess, since I’ve never published in them but would like to at least once in my life 🙃 /1 2/ so for that reason I can’t tell the main, new discovery right now. But I can say this:

In the Apollo era the thinking was that the rate of soil erosion is controlled by conservation of momentum. It turns out this is wrong.
May 15, 2023 4 tweets 2 min read
The whole reason I work on space is to preserve Earth — space has and will in the future greatly benefit Earth. **But** we have to accept that launching to space will have some minor environmental impact. The question is… /1 2/ … “Is space worth it?” The answer is yes.

NASA’s launch site is also on a wildlife refuge. There is (sadly!) some harm to wildlife both from launching and from 1000s of workers driving to/from work on the refuge every day. But as a nation we need to have launch sites. ImageImage